1. Field of the Invention
This invention relates to well flow control apparatus and more particularly to side pocket mandrels and flow control devices used therein for controlling wells which are produced by a type of secondary recovery commonly known in the industry as "gas lift."
2. Description of the Prior Art
Side pocket mandrels have been used in practicing gas lift techniques for recovery of oil from wells for many years. These mandrels are connectable in a well tubing string to become a part thereof. Typically, they have a main bore or flow passage running their entire length and are provided with an offset belly in which is located a receptacle having a bore extending alongside the main bore. The receptacle bore is adapted to receive a flow control device such as, for instance, a gas lift valve, a check valve, a dummy valve, or the like. One or more ports in the wall of the receptacle provide fluid communication between the interior of the receptacle and the region exterior of the well tubing. The side pocket mandrels are scientifically spaced at appropriate depths in the well at which it is desired to have flow take place between the tubing and the annulus exterior thereof. A flow control device normally occupies each of the side pocket receptacles in a gas lift well, and proper adjustment of such devices results in lift gas, which is injected into the tubing-casing annulus at the surface, being admitted into the tubing at the proper depth to aerate the oil rising therein and aid in lifting it to the surface in the most efficient manner. When no flow control device is present in the receptacle of a side pocket mandrel in a well, the annulus and tubing communicate freely, that is, if the side pocket mandrel is of the standard type. A typical side pocket mandrel is illustrated and described in U.S. Pat. No. 3,827,490 issued Aug. 6, 1974 to Howard H. Moore and Harold E. McGowen, Jr. Illustrated and described in U.S. Pat. No. 4,066,128, which issued Jan. 3, 1978 to Jerry B. Davis and Guy W. Gant, is an improved side pocket mandrel and flow control device, the side pocket receptacle of which is provided with a sliding sleeve valve controlling the receptacle's lateral ports. The sliding sleeve valve is moved to open position when the flow control is installed, and the sleeve valve is returned to and left latched in closed position when the flow control device is removed. Thus, when no flow control device is present, communication between annulus and tubing is prevented.
The structure of the device of U.S. Pat. No. 4,066,128 is such that the external seals carried on the flow control device seal in the bore of the sleeve valve which in turn seals in the receptacle bore device, making the flow control device, of necessity, rather small in diameter and having a limited capacity flow passage therethrough for the conduction of lift gas. The seals carried on the flow control device are appreciably smaller in diameter than the seals carried by the sliding sleeve valve. The present invention overcomes these shortcomings by providing a side pocket mandrel having a sliding sleeve valve and accepting a flow control device having seals the same size as those on the sliding sleeve valve and sealing in the receptacle bore just as do the seals on the sliding sleeve valve. The flow control device, thus, can be a standard size and have a standard flow passage through it.